As world demand for food has tripled, so too has the use of water for irrigation. As a result, the world is incurring a vast water deficit. But because this deficit takes the form of aquifer overpumping and falling water tables, it is nearly invisible. Falling water levels are often not discovered until wells go dry. 20

The world water deficit is historically recent. Only within the last half-century, with the advent of powerful diesel and electrically driven pumps, has the world had the pumping capacity to deplete aquifers. The worldwide spread of these pumps since the late 1960s and the drilling of millions of wells, mostly for irrigation, have in many cases pushed water withdrawal beyond the aquifer’s recharge from rainfall. As a result, water tables are now falling in countries that are home to more than half of the world’s people, including China, India, and the United States—the three largest grain producers. 21

Groundwater levels are falling throughout the northern half of China. Under the North China Plain, they are dropping one to three meters (3–10 feet) a year. In India, they are falling in most states, including the Punjab, the country’s breadbasket. And in the United States, water levels are falling throughout the southern Great Plains and the Southwest. Overpumping creates a false sense of food security: it enables us to satisfy growing food needs today, but it almost guarantees a decline in food production tomorrow when the aquifer is depleted. 22

With 1,000 tons of water required to produce 1 ton of grain, food security is closely tied to water security. Seventy percent of world water use is for irrigation, 20 percent is used by industry, and 10 percent is for residential purposes. As urban water use rises even as aquifers are being depleted, farmers are faced with a shrinking share of a shrinking water supply. 23

At the same time that water tables are falling, temperatures are rising. As concern about climate change has intensified, scientists have begun to focus on the precise relationship between temperature and crop yields. Crop ecologists at the International Rice Research Institute in the Philippines and at the U.S. Department of Agriculture (USDA) have jointly concluded that with each 1-degree Celsius rise in temperature during the growing season, the yields of wheat, rice, and corn drop by 10 percent. 24

Over the last three decades, the earth’s average temperature has climbed by nearly 0.7 degrees Celsius, with the four warmest years on record coming during the last six years. In 2002, record-high temperatures and drought shrank grain harvests in both India and the United States. In 2003, it was Europe that bore the brunt of the intense heat. The record-breaking August heat wave that claimed 35,000 lives in eight nations withered grain harvests in virtually every country from France in the west through the Ukraine in the east. 25

The Intergovernmental Panel on Climate Change projects that during this century, with a business-as-usual scenario, the earth’s average temperature will rise by 1.4–5.8 degrees Celsius (2–10 degrees Fahrenheit). These projections are for the earth’s average temperature, but the rise is expected to be much greater over land than over the oceans, in the higher latitudes than in the equatorial regions, and in the interior of continents than in the coastal regions. This suggests that increases far in excess of the projected average are likely for regions such as the North American breadbasket—the region defined by the Great Plains of the United States and Canada and the U.S. Corn Belt. Today’s farmers face the prospect of temperatures higher than any generation of farmers since agriculture began.

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